The invention generally relates to inflation devices used in medical procedures, and more particularly, to inflation control systems suitable for controlling the inflation and deflation of balloons or other inflatable devices used in medical procedures, such as balloon catheters used in angioplasty procedures.
Dilatation balloon catheters have been used in increasing numbers in angioplasty procedures to dilate or enlarge blood vessels that have been partially or almost completely blocked by stenosis (a narrowing of the vessel due to injury or disease). Angioplasty procedures have been used to treat stenoses in coronary arteries, peripheral arteries, urethral passages, fallopian tubes, etc. Particularly, the procedure for dilating coronary arteries, referred to as percutaneous transluminal coronary angioplasty (PTCA), has provided an effective and less traumatic treatment technique than coronary by-pass surgery or other surgical treatment methods.
In a typical angioplasty procedure, a guiding catheter is percutaneously introduced into the vascular system of a patient and is directed to a point near the site of the stenosis. Subsequently, a guidewire and a dilatation catheter having an inflatable balloon mounted on the distal end thereof are introduced through the guiding catheter with the guidewire slidably disposed within an inner lumen of the dilatation catheter. The guidewire is advanced out of the distal end of the guiding catheter and is maneuvered into the patient's vasculature containing the stenosis to be dilated, and is then advanced beyond the stenosis. Thereafter, the dilatation catheter is advanced over the guidewire until the dilatation balloon is located across the stenosis. Once in position, the dilatation balloon is inflated to a predetermined size, typically the same size as the inner diameter of the blood vessel at that location, by radiopaque liquid at relatively high pressures (e.g., generally greater than about four atmospheres). The inflated, pressurized balloon radially compresses the atherosclerotic plaque of the stenosis against the inside of the vessel wall to thereby dilate the lumen of the vessel and allow increased blood flow through the vessel.
In a typical PTCA procedure, the balloon is inflated and deflated several times with the pressure maintained for several seconds during each inflation, until the desired patency in the blood vessel is obtained. The physician typically monitors a timing device to control the duration of each inflation and the duration between inflations. Each inflation of the balloon interferes with the blood supply circulation; therefore, the duration must be kept as short as possible, yet must still be long enough to obtain the results desired. The duration between inflations is monitored to allow enough time for the blood supply to reestablish itself before the next inflation. After the procedure has been completed, the balloon is deflated for the final time and maintained under negative pressure so that the dilatation catheter can be withdrawn from the patient and the blood flow resumed through the dilated vessel.
To inflate or deflate the balloon, the physician typically uses an inflation device, such as a syringe, placed in fluid communication with the interior of the balloon. The physician uses one hand to grasp the syringe body and the other hand to maneuver the plunger to pressurize or depressurize the inflation fluid as required. Manually operated syringe-type inflation systems of the type described are manufactured and sold by Advanced Cardiovascular Systems, Inc. of Santa Clara, Calif. under the trademark INDEFLATOR.
Such manual inflation systems have proven to be of great value in conducting angioplasty procedures. Some systems include a pressure sensor with a display that indicates to the operator the fluid pressure in the catheter/balloon. A balloon pressure display allows the physician to monitor whether the arterial plaque causing the stenosis is subjected to a sufficiently high pressure to cause compression of the plaque. Such a display also allows the physician to monitor the pressure to ensure that the balloon pressure limits specified by the manufacturer are not exceeded. Furthermore, if the pressure display indicates a sudden and unexpected decrease in pressure, the physician may be alerted so that any necessary remedial action can be taken.
However, manual systems typically require the physician to use both hands to control the inflation and deflation processes. Each time an adjustment in the location of the balloon in the patient's vessel must be made, the physician must move at least one hand from the inflation control system to the catheter to accomplish the relocation of the balloon, and must then return to the inflation system with both hands. Rather than having to use both hands on the inflation device, it would be preferable for the physician to only use one hand thereby leaving the second hand free to control the position of the catheter in the vessel or to perform other tasks, as needed.
A further consideration with manual inflation systems is the ease with which the system can be used. In manual systems that require a substantial amount of hand strength to maneuver the syringe plunger for developing enough pressure in the balloon to compress the plaque, the physician may experience hand fatigue as a result of operating such an inflation device for several inflation and deflation cycles, each lasting several seconds.
Inflation control systems using a motor drive to control the position of a plunger in a syringe to control the balloon pressure have been described. Such motor drive inflation systems reduce or eliminate the need for the physician to manually control the position of the plunger in the syringe. The physician instead controls the movement of a motor through an electrical switch. That motor performs the work of moving the syringe plunger. Usually only one hand is needed to operate the electrical switch or switches needed for motor control thus leaving one of the physician's hands free to locate the catheter or perform other tasks. Such systems can provide the ability to inflate or deflate the balloon catheter at a precise moment during the maneuvering of the catheter in the patient's vessel with relatively precise control over the rates of inflation and deflation.
Motor driven inflation systems typically use a syringe or syringe-type fluid reservoir for containing the fluid that is to be pressurized to control balloon inflation. Typically, the syringe comprises a barrel with a movable plunger to control the volume in the barrel thereby controlling the pressure developed. At the far end of the barrel, a smaller diameter nozzle is used to make fluid communication with a fluid line. The fluid line is connected to the dilatation catheter at the start of the procedure. However prior to that time, the syringe assembly must be prepared for use.
Typically, the syringe assembly is provided empty. That is, no radiopaque fluid is present in the barrel of the syringe. The operator would usually remove the syringe assembly from its packaging, immerse the fluid line in the fluid to be used for the angioplasty procedure, and draw some of that fluid into the fluid line and syringe barrel. Air would then be expelled. To accomplish this preparation, a stopcock is provided at the distal end of the fluid tubing. The stopcock has three positions. The first of closed, the second is open to a connected catheter, and the third is vent to atmosphere. Thus the syringe assembly has three main components: a syringe, a fluid tubing, and a stopcock.
After the syringe assembly has been fully prepared, it is then mounted to the motor drive instrument and the plunger is engaged with the drive mechanism. In some prior cases, this engagement procedure can require the manipulation of mechanical devices by the instrument operator to connect the drive device to the plunger so that the plunger's position will be under motor control. The manipulation of complex devices to achieve engagement or the requirement of significant strength to manipulate those devices are both undesirable. It is desirable that the engagement process be straight forward and require little effort on the part of the operating personnel. After engagement has been effected, the syringe is connected to the dilatation catheter by means of a luer connector and the stopcock opened for fluid communication with the catheter.
Relatively high pressures are developed in dilatation procedures, in some cases, over ten atmospheres. Additionally, negative pressure must be drawn in the syringe assembly to assure collapse of the dilatation balloon for withdrawal from the patient. Thus, the syringe assembly must be capable of withstanding these high positive pressures and negative pressures. Should the syringe, tubing, or stopcock have a pressure leak and be unable to develop ten atmospheres of pressure during a procedure, the physician may be forced to replace the syringe assembly with another during the procedure. This would require preparing the new syringe assembly, including drawing fluid into the syringe, and the expulsion of any air trapped in the new syringe. The removal of the old assembly, the preparation of the new assembly and its mounting to the instrument can undesirably delay the dilatation procedure.
Prior to commencement of the angioplasty procedure, it would be useful to determine whether the selected syringe assembly can support the pressures required during the procedure. If a syringe assembly unable to support these pressures could be identified prior to the start of the procedure, it could be replaced at that time rather than during the procedure.
Hence those skilled in the art have recognized the need for an engagement system for mating a drive device with the syringe plunger of a syringe that is relatively simple and easy to operate. Also, those skilled in the art have recognized the need for an automated pressure integrity check of a syringe before a dilatation procedure begins so that the ability to reach the desired pressures during a medical procedure can be verified before the procedure is begun. The present invention fulfills these needs and others.